3d Cloud Morphingng

You will have to animate vertices via script.

Here is a c sharp version from the community: http://www.unifycommunity.com/wiki/index.php?title=MorphTargets

Here is a javascript version from the community: http://www.unifycommunity.com/wiki/index.php?title=MeshMorpher

For your example you would need a cloud with a known number of vertices, let's say it has 542 vertices. If you would like to morph the cloud mesh to, let's say, a pen mesh, then pen mesh would have to have the same number of vertices as the cloud, since you are moving all the vertices from one object into the position of the vertices of another mesh. You will have to average your normals on import because the vertice count will increase in order to store hard-edged normals. I haven't used these scripts but I suspect if your shapes are wildly different you will run into a lot of problems. For instance a sphere will not morph into the eiffel tower or into a car. The triangles will stretch and normals will be flipped. On the other end of the spectrum a cube will morph very well into a rectangular box.

In my opinion, simple morphing clouds into various shapes will prove cumbersome, error-prone, and the results will most likely be lackluster.

That said, you will find great success doing simple model swaps. Make a cloud object. Make a separate pen object. Enable the cloud in unity and disable the pen. At the time of "morphing", set the position and rotation of the pen to the position and rotation of the cloud, then disable the cloud and enable the pen. You can even play a sound and spawn some particles to easy the visual switch on the eye. You could even add a cute little scaling animation on the pen, like it is bouncing into existence.

Good luck!